There's strong precedence for associating file extensions with content types. And it allows static files to map 1:1 to URLs.

I agree though that I was too harsh, I didn't realize it was written in 1998 when HTML was still new. I probably first read it around 2010.

But now that we have hindsight, I think it's safe to say .html files will continue to be supported for the next 50 years.